1. Field of the Invention
The present invention relates to an apparatus for manufacturing a wrinkled pipe having a highly accurate external diameter and, more particularly, to a wrinkled pipe manufacturing apparatus capable of manufacturing a highly accurate wrinkled pipe having no rise of the curled end portion even if the pipe is a curled pipe of multiple layers.
2. Description of the Prior Art
The wrinkled pipe manufacturing apparatus has been proposed in Japanese Patent Publication No. 44-24746 (Bulging Apparatus), Japanese Patent Laid-Open No. 59-133021 (Method of and Apparatus for Manufacturing Strung Pipe) or Japanese Patent Laid-Open No. 63-207421 (Method of and Apparatus for Manufacturing Beaded Pipe).
Of these, the proposal of Japanese Patent Publication No. 44-24746 works and shapes the necessary wrinkled portion by one step of performing the bulging of the beaded portion due to an internal pressure and the axial compression by a mold simultaneously.
According to the proposal of Japanese Patent Laid-Open No. 59-133021, the strung pipe is manufactured by inserting two mandrel rods interposing an elastic member into a pipe, by pushing one of the mandrel rods toward the other to deform the elastic member thereby to pull and bulge a portion of the pipe, and then by shaping the bulged portion in conformity with a bending mold receiving the bulged portion.
According to the proposal of Japanese Patent Laid-Open No. 63-207421, on the other hand, the beaded pipe is manufactured by arranging a pressure medium for applying an internal pressure to the inside of a work, by arranging molding elements having a bead shaping recess outside of the work for relatively moving toward and apart from the pipe axis, and by plastically deforming the work into the bulged state to move the molding elements toward each other.
Of the systems thus far described according to the prior art, the proposal of Japanese Patent Laid-Open No. 44-24746 is required to prepare its mold according to the length of the pipe and the beam number of the wrinkles, to have its workable pipe length restricted and to have an expensive mold.
Both the proposals of Japanese Patent Laid-Open Nos. 59-133021 and 63-207421 can have a relatively high degree of freedom in the beat number of wrinkles but has its elastic member extending through the mandrels. In order to retain the strength of the mandrels and the space for the elastic member, the mandrel portions are so difficult to thin that the diameter of the workable pipe is about 16 mm at the least.
Since, moreover, the molding portions have the bead shaping grooves, the external diameter and pitch of the beads are restricted to limit the degree of freedom for the bead shape. Since, moreover, the pipe is fixed at its bulging two ends by the mold, it cannot move sufficient in the axial directions during its bulging operations so that the bead ridge is thinned whereas the elastic member is forced to slide and is seriously worn. Since the elastic member will bulge into the mold of the two proposals, the mold is required to have a high molding force so that the elastic member is subject to an excessive force and will be worn.
When the wrinkles are to be continuously molded, the elastic member is compressed from the wrinkle side to bite into the gaps of the wrinkles so that it is seriously worn.
According to the proposal of Japanese Patent Laid-Open No. 63-207421, moreover, the bulging portion is axially compressed together with the elastic member to cause a trouble that the elastic member is torn to pieces.